Professor Hannele Korhonen from the Finnish Meteorological Institute heads a research group which received a €1.5 million grant in January from a research programme on rain in the United Arab Emirates.

Photo: Ulla Sainio

Can researchers make it rain?

TWO-THIRDS LACK WATER

Only 2.5% of the Earth’s water is potable. And of that, only a fraction is easily available to humans. As the standard of living increases and the population grows, so will water consumption, while climate change further deteriorates the situation in many areas already struggling with drought.

According to the UN, two-thirds of the world’s population will live in areas with limited access to water by the year 2025. In such a world, even a small relief could help millions.

Some areas struggle with torrential rains, others with drought. In hot areas, rain is precious. Could artificial rain help in times of drought?

Water is constantly evaporating into the atmosphere from our seas, lakes and other waterways. If the conditions are right, it forms clouds. And if the air cools enough as it rises, the water vapour molecules will begin to form droplets or ice crystals. If a droplet becomes large enough, gravity may overcome the air currents holding it up, and if the droplet or crystal doesn’t evaporate as it falls, there will be rain.

In hot areas, such as on the Arabian Peninsula, the evaporation of water is not a problem – the temperature during the day is always above 20 degrees Celsius, even in winter, with summer temperatures often going above 45 degrees. Clouds do form, but the water in them rarely makes it back to the ground: there are, on average, only about five to ten rainy days per year, and some years have no rain at all.

The oil-rich United Arab Emirates desalinates billions of litres of sea water every day, but this is expensive and further contributes to global warming, as the desalination plants typically need oil or natural gas to function.

This is why the country is now struggling to discover how the water in the skies could be brought back to the ground.

Artificial rain

Meteorology and physics researchers from the Kumpula Campus are about to head to the dry Arabian Peninsula to see what kinds of aerosol particles could generate rain clouds.

The Finns intend to survey the role of aerosol particles in the formation of clouds and rain. Aerosols are liquid or solid particles that float in the air. They are released into the atmosphere from traffic, sandy deserts and forest fires. Some of them become cores around which rain drops and ice crystals form.

The research may reveal whether seeding aerosol particles into the clouds could help produce rain. If a suitable particle is found to serve as the core for raindrops in the climate of the UAE, these particles could be sprinkled onto the clouds from planes to generate artificial rain.

Such manmade rain would surely be popular in other dry and hot areas as well. It could be a key tool in relieving global poverty and hunger.

But there is still a long way to go. Much more research is needed to confirm the efficacy of cloud seeding to provide help where it is needed.

Cloud seeding

The concept of making rain is not new. People have tried to change the weather throughout history through a variety of rituals, and science-based efforts to control rain have been made since the 1930s.

Research into rainmaking was still generously funded during the 1970s and 80s, but enthusiasm gradually waned in the absence of reliable results, according to Hannele Korhonen, research professor at the Finnish Meteorological Institute.

“But cloud seeding experiments keep being conducted, based on previous research and hope. They are being done in up to 50 countries, even though the results of the method have been difficult to establish.”

Silver iodide is typically used in cloud seeding, as its structure is similar to that of ice crystals. Silver iodide was used during the Sochi and Beijing Olympics – the substance was released into the clouds before they reached the stadium to make them rain where it would cause no trouble.

At least, that is the intention.

“The problem is that once the cloud has been seeded, there is nothing to compare the results to,” Korhonen says.

Another problem is that silver iodide is toxic, even though it is used in extremely low concentrations in cloud seeding.

Crystal cores

The Finnish researchers are going to the UAE primarily to conduct basic research – to find out whether cloud seeding can be scientifically justified, and if so, what kinds of aerosol particles should be used to generate rain. The work will be based on measurements and simulations; nothing will be released into the clouds at this stage.

The efforts to find the most suitable particles are led by Hanna Vehkamäki, professor of aerosol physics at the University of Helsinki. Her group will develop a molecular simulation to discover what kinds of particle surfaces are likely to generate ice.

“The atmosphere has an untold amount of particles, and only a tiny fraction of them, perhaps one tenth of a percentage, can serve as cores for ice crystals. It’s like looking for a needle in a haystack,” says Vehkamäki.

Atom by atom

The size range of the aerosol particles is astounding. While the smallest are a five-thousandth of the width of a human hair in diameter, others can be more than twice the width of a hair. Neither can the particles be easily divided into those that attract and those that repel water – the solution lies in microscopic details which are a formidable task to image precisely, even for today’s supercomputers. The researchers would have to know in which position the first water molecule collides with the aerosol particle.

“We have to build the model atom by atom and molecule by molecule,” says Vehkamäki.

The particle simulations are just a tiny component of a vast research topic. The Finnish Meteorological Institute is in charge of a larger sector, cloud modelling. This modelling hopes to discover how the particles seeded into the clouds impact the properties of the clouds and rain formation in various circumstances.

Relief for dry areas?

Changing the weather sounds like a foolhardy proposition. What could the consequences be? The researchers say that they have also considered this. Would artificially induced rain in one area mean no rain in another, or would the clouds just evaporate into the atmosphere without any rain? According to Korhonen, these are controversial topics.

Nevertheless, the impacts would be geographically limited – the intention is to influence the weather, not the climate. But Korhonen and Vehkamäkin are not even completely sure that humans can change the weather at all.

Bringing hope is a good thing, but humanity still has to wait for major strides in creating rain.

“I don’t think that making rain would solve the problems in drought-ridden areas, but it could be part of a solution, or at least bring some relief somewhere,” says Vehkamäki.

Measure twice, model once

Before Hannele Korhonen’s and Hanna Vehkamäki’s groups can get properly started with the modelling and simulations, they will need measurement data from the UAE. The data will be provided by Professor Heikki Lihavainen's group from the Finnish Meteorological Institute, which will begin its field work in the summer.

The researchers’ previous measuring campaign on the Arabian Peninsula ended two years ago, but now they are returning with LIDAR equipment, which can provide increasingly precise remote sensing data from the atmosphere. LIDAR is an acronym of Light Detection and Ranging.

LIDAR sends out a laser pulse into the sky and measures how its light scatters when it reflects back. This way researchers can find out, for example, how high the aerosol particles are, and at which height they begin to generate clouds. The measuring equipment on the ground can also give detailed information about the small particles in the atmosphere.

“We measure the same kinds of natural processes that are observed in Finland. The conditions in the United Arab Emirates are different, but the basic equations hold true. This is an opportunity for us to develop our understanding and to apply the information in our own model development,” says Lihavainen.

The measuring equipment is due to be fully operational in the UAE in July, which Lihavainen considers an optimistic schedule. But they will have to do their best to achieve it, as a Japanese research group which received funding from the same research programme will begin its intense measuring operations in the same area in August.

“They intend to bring a plane to measure the properties of particles and clouds in the atmosphere.”

Can’t export rain

Text: Arja Tuusvuori

Professor Miikka Dal Maso from the Tampere University of Technology got his start at the University of Helsinki, in Professor Markku Kulmala’s aerosol physics research group.

“Physics is a good choice for a curious person who’s interested in natural phenomena and the world at large.”

Dal Maso is interested in the ways the particle and gas emissions in the atmosphere change during their lifespan. His group provides their skills in mathematical modelling to the project. The goal is to determine as precisely as possible how various climate conditions influence the way particles form and change.

Most of the work is done behind a desk in Tampere, but the group also intends to visit the United Arab Emirates.

“It’s always useful and exciting to see what kind of conditions my work relates to. We are working together with a local university, and we intend to promote education in aerosol research. The plan is to produce at least one doctoral dissertation relating to the topic.”

Dal Maso advises caution in terms of changing the climate. You can’t export rain; the atmosphere is too complex for that.

“We can’t make it rain if there’s no humidity in the air. Even though humans are changing the climate indirectly and unintentionally, we are not yet fully capable of controlling the weather.

“Rain needs the right conditions to happen.”

This article was published in Finnish in the Y/05/17 issue of Yliopisto magazine.